There's a really good list of all the conditional defines that have been defined in Delphi (and even Turbo Pascal) over the years at Delphi Wiki. But if you want to see how to use them in code or add a few more for your self to test, here's some code to get you started.

This simple project compiles in all the recent versions of Delphi. If you want to compile it in earlier versions, you'll have to remove a line in the main project file--but you'll quickly realize that when you go to compile.

FREEWARE from Cornelius Concepts.